Method and Apparatus for Operating Buffer State Report in Wireless Communication System Supporting Device to Device Communication

1. A method of supporting a buffer status report (BSR) associated with a device-to-device (D2D) communication, the method comprising: establishing a radio resource control (RRC) connection with an evolved NodeB (eNB) and receiving configuration information associated with a D2D communication from the eNB, the configuration information comprising information of a resource allocation mode for a D2D data transmission and information of a timer associated with a BSR for a D2D data transmission; determining, by a user equipment (UE), a radio link failure (RLF), the RLF being associated with a connection problem of the RRC connection; initializing a re-establishment process for the RRC connection; canceling all BSRs for a D2D data transmission in response to the determined RLF, the canceled BSRs for a D2D data transmission being associated with a D2D data transmission scheduled by the eNB; initializing the timer associated with a BSR for a D2D data transmission; determining, by the UE, a change from the resource allocation mode for a D2D data transmission to a resource selection mode when an exceptional case occurs; and in the resource selection mode, selecting, by the UE, a resource for transmitting D2D data from a resource pool, wherein the exceptional case comprises: a case where upon detecting the RLF, the initialization of the re-establishment process for the RRC connection has been initiated and a T311 timer associated with the re-establishment process for the RRC connection has been started, receiving information of CommTxPoolExceptional for a D2D data transmission for the exceptional case, wherein the CommTxPoolExceptional is information of a resource pool for a D2D data transmission when the exceptional case occurs.

2. The method of claim 1 , wherein initializing of the timer associated with a BSR for a D2D data transmission comprises: initializing a periodic BSR-timer and a retransmission BSR-timer (retx BSR-timer).

3. The method of claim 2 , wherein initializing of the periodic BSR-timer and the retx BSR-timer comprises: stopping the periodic BSR-timer and the retx BSR-timer and setting timer values of the periodic BSR-timer and the retx BSR-timer as zero.

4. The method of claim 1 , further comprising: receiving information of a resource selection mode; and in the resource selection mode, selecting, by the UE, a resource for transmitting D2D data from a resource pool indicated by the information of a resource selection mode.

5. The method of claim 1 , further comprising: receiving the CommTxPoolExceptional from the eNB through a broadcast channel.

6. The method of claim 1 , wherein the CommTxPoolExceptional is included in a System Information Block (SIB).

7. The method of claim 1 , further comprising: transmitting D2D data by selecting a resource by the UE based on information of CommTxPoolExceptional, the CommTxPoolExceptional indicating resource pool information for a D2D data transmission when the exceptional case occurs.

8. A user equipment (UE) to support a buffer status report (BSR) associated with a device-to-device (D2D) communication, the UE comprising: a wireless transceiver to establish a radio resource control (RRC) connection with an evolved NodeB (eNB) and to receive configuration information associated with a D2D communication from the eNB, the configuration information comprising information of a resource allocation mode for a D2D data transmission and information of a timer associated with a BSR for a D2D data transmission; and a processor configured to determine a radio link failure (RLF), the RLF being associated with a connection problem of the RRC connection, to initialize a re-establishment process for the RRC connection, to cancel all BSRs for a D2D data transmission in response to the determined RLF, the canceled BSRs for a D2D data transmission being associated with a D2D data transmission scheduled by the eNB, and to initialize the timer associated with a BSR for a D2D data transmission, wherein the processor is configured to determine a change from the resource allocation mode for a D2D data transmission to a resource selection mode when an exceptional case occurs, wherein in the resource selection mode, the processor is configured to select a resource for transmitting D2D data from a resource pool, wherein the exceptional case comprises: a case where upon detecting the RLF, the initialization of the re-establishment process for the RRC connection has been initiated and a T311 timer associated with the re-establishment process for the RRC connection has been started, wherein the wireless transceiver receives information of CommTxPoolExceptional for a D2D data transmission for the exceptional case, and wherein the CommTxPoolExceptional is information of a resource pool for a D2D data transmission when the exceptional case occurs.

9. The UE of claim 8 , wherein initializing of the timer associated with a BSR for a D2D data transmission comprises: the processor initializes a periodic BSR-timer and a retransmission BSR-timer (retx BSR-timer).

10. The UE of claim 9 , wherein initializing of the periodic BSR-timer and the retx BSR-timer comprises: the processor stops the periodic BSR-timer and the retx BSR-timer and sets timer values of the periodic BSR-timer and the retx BSR-timer as zero.

11. The UE of claim 8 , wherein the wireless transceiver receives information of a resource selection mode, and wherein in the resource selection mode, the processor is configured to select a resource for transmitting D2D data from a resource pool indicated by the information of a resource selection mode.

12. The UE of claim 8 , wherein the wireless transceiver receives the CommTxPoolExceptional from the eNB through a broadcast channel, wherein the CommTxPoolExceptional is included in a System Information Block (SIB).

13. The UE of claim 8 , wherein the wireless transceiver transmits D2D data by selecting, by the processor, a resource based on information of CommTxPoolExceptional, the CommTxPoolExceptional indicating resource pool information for a D2D data transmission when the exceptional case occurs.

14. A method of supporting a buffer status report (BSR) associated with a device-to-device (D2D) communication, the method comprising: establishing a radio resource control (RRC) connection with an evolved NodeB (eNB) and receiving configuration information associated with a D2D communication from the eNB, the configuration information comprising information of a resource allocation for a D2D data transmission; operating, based on the information of the resource allocation for a D2D data transmission, a user equipment (UE) in a first transmission mode for a D2D communication, the first transmission mode corresponding to an eNB resource allocation mode in which a D2D data transmission resource is allocated by the eNB; determining, by the UE, an exceptional case; transitioning, for a time period, from the first transmission mode to a second transmission mode in response to determining the exceptional case, the second transmission mode corresponding to a UE resource selection mode in which the UE selects, from a resource pool, a resource for transmitting D2D data; and canceling at least one triggered BSR for a D2D data transmission in response to determining the exceptional case, the canceled BSR for a D2D data transmission being associated with a D2D data transmission scheduled by the eNB, wherein the exceptional case comprises: a case where upon detecting a radio link failure (RLF), an initialization of re-establishment process for the RRC connection has been initiated and a T311 timer associated with the re-establishment process for the RRC connection has been started, receiving information of CommTxPoolExceptional for a D2D data transmission for the exceptional case, wherein the CommTxPoolExceptional is information of a resource pool for a D2D data transmission when the exceptional case occurs.

15. The method of claim 14 , further comprising; initializing a timer associated with a BSR for a D2D data transmission in the second transmission mode; and returning, after the time period, to the first transmission mode, wherein the initialized timer restarts when the UE transitions into the first transmission mode from the second transmission mode.

16. The method of claim 14 , wherein a periodic BSR-timer and a retransmission BSR-timer (retx BSR-timer) are reset in response to determining the exceptional case.